Thermally degradable epoxy underfills for flip-chip applications

ABSTRACT

A reworkable epoxy underfill is provided for use in an electronic packaged system which incorporates an integrated circuit, an organic printed wire board, and at least one eutectic solder joint formed therebetween. An exemplary embodiment of the encapsulant includes: a cycloaliphatic epoxide; an organic hardener; and a curing accelerator; wherein said cycloaliphatic epoxide includes a carbonate or carbamate group. The encapsulant can also include a filler, such as a silica filler. A method is also provided for forming the aforementioned reworkable epoxy underfills.

RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional Pat.Application Ser. No. 60/193,356, filed Mar. 29, 2000.

FIELD OF THE INVENTION

[0002] This invention relates to thermally reworkable epoxy resincompositions, and more particularly to thermally reworkable carbamate orcarbonate epoxide resin compositions which degrade at temperaturessignificantly lower than traditional cycloaliphatic epoxy resins.

BACKGROUND OF THE INVENTION

[0003] In the field of electronic packaging and, in particular, thefield of integrated circuit (IC) chip interconnection, the desirabilityof incorporating high input/output (I/O) capability and short ICinterconnects, among others, typically has led to the adoption of theflip-chip technique of IC chip interconnection. Generally, the flip-chiptechnique involves electrically interconnecting an IC chip and asubstrate with the use of solder joints which are disposed between theIC chip and the substrate.

[0004] As initially practiced, the flip-chip technique oftentimesutilized relatively high cost materials, such as high lead solder andceramic substrate. However, the desire to reduce costs has prompted theuse of less expensive materials, such as flip-chip on board (FCOB),which typically utilizes eutectic solder and organic printed wiringboard (PWB). While reducing material costs, the use of FCOB packagedsystems has accentuated the problem of coefficient of thermal expansion(CTE) mismatch between the IC chip and the organic substrate of theFCOB, particularly when large IC chips and fine pitch, low profilesolder joints are utilized. Due to the CTE mismatch between silicon ICchips (2.5 ppm/° C.) and organic substrates, i.e., FR-4 PWB (18-24 ppm/°C.), temperature cycle excursions experienced by the FCOB generatetremendous thermo-mechanical stress at the solder joints and,subsequently, can result in performance degradation of the packagedsystem.

[0005] It is also known in the prior art to fill the spaces or gapsremaining between an IC chip and substrate which are not occupied bysolder with an underfill composition. The undefill is an adhesive, suchas a resin, that serves to reinforce the physical and mechanicalproperties of the solder joints between the IC chip and the substrate.The underfill typically not only provides fatigue life enhancement of apackaged system, but also provides corrosion protection to the IC chipby sealing the electrical interconnections of the IC chip from moisture,oftentimes resulting in an improvement in fatigue life of ten to overone hundred fold, as compared to an un-encapsulated packaged system.

[0006] Heretofore, cycloaliphatic epoxies, typically combined withorganic acid anhydrides as a hardener, have been used in flip-chippackaged systems as an underfill. This is primarily due to the lowviscosity of cycloaliphatic epoxies prior to curing, as well as theiracceptable adhesion properties after curing. Other epoxies such asbisphenol A or F type or naphthalene type can also be used in theunderfill formulations. Additionally, silica has been utilized as afiller in these underfill formulations, i.e., up to 70% (by weight), inorder to lower the CTE of the epoxy resin. By way of example, thematerial properties represented in Table 1 typically are exhibited bytypical prior art epoxy underfill compositions. TABLE 1 TypicalUnderfill Properties Solids Content 100% Form Single component,pre-mixed Coefficient of Thermal Expansion (α₁) 22-27 ppm/° C. Tg >125 °C. Cure Temperature <165 ° C. Cure Time <30 min. Working Life (@ 25° C.,visc. Double) >16 hrs. Viscosity (@ 25° C.) <20 kcps Filler Size 95% <15μm Filler Content <70 wt % Alpha Particle Emission <0.005 counts/cm²/hr.Hardness (Shore D) >85 Modulus 6-8 Gpa Fracture Toughness >1.3Mpa-m^(1/2) Volume Resistivity (@ 25° C.) >10¹³ ohm-cm DielectricConstant (@ 25° C.) <4.0 Dissipation Factor (@ 25° C., 1 kHz) <0.005Extractable Ions (e.g. Cl, Na, K, Fe, etc.) <20 ppm total MoistureAbsorption (8 hrs. boiling water) <0.25%

[0007] Frequently, defects in a chip or circuit board are not discovereduntil after assembly of an electrical component using an underfilladhesive. Heretofore, it has generally been commercially impractical toseparate and clean the chip and/or board so that the non-defectivecomponents can be reused. This results in increased production costs dueto the waste of otherwise usable components. An effective way to addressthis problem is to make the flip-chip devices reworkable under certainconditions.

[0008] One method which has been developed in an attempt create areworkable flip-chip device has been to incorporate a non-stick releasecoating on the boundary surface between a chip and a substrate. Forexample, U.S. Pat. No. 5,371,328 discloses a reworkable flip-chip typeof circuit module using a non-stick release coating on all surfacesintermediate of the chip and the substrate. While this non-stick releasecoating may be suitable in some applications, it is likely that the useof such a release coating may reduce the adhesion of all the interfacesincluding those of the underfill to chip and underfill to substrate.These adhesions are important to the reliability of the flip-chipinterconnections. Accordingly, this approach is not ideal for use inflip-chip applications.

[0009] Another approach to providing a reworkable flip-chipinterconnection is to use a reworkable underfill. Presently, thematerials that are undergoing development for reworkable underfills canbe classified into two categories: chemically reworkable underfills andthermally reworkable underfills.

[0010] Chemically reworkable underfills generally require the use ofharsh acids and/or bases. For example, U.S. Pat. No. 5,560,934, issuedto Afzali-Ardakani et al., discloses epoxy compositions that are solublein an organic acid after curing. Utilizing relatively strong chemicalssuch as acids (or bases) during reworking, however, oftentimes leads toa messy, time-consuming rework process. Additionally, it has been foundthat the use of chemicals during the rework process typically makeslocalized repair of a packaged system difficult and, sometimes,impossible. Therefore, it is believed that use of a thermal reworkprocess would avoid these problems and offer the possibility of a quick,clean, and localized rework process.

[0011] U.S. Pat. No. 5,659,203, issued to Call et al., discloses areworkable flip-chip module utilizing a specially defined thermoplasticresin as an encapsulant. The thermoplastic resin, such as polysulfone,polyetherimide, etc., possesses a high glass transition temperature(Tg), e.g., 120° C.<Tg<220° C., and must be either dissolved in asolvent or heated above its melting point during the encapsulationprocess. Therefore, use of these thermoplastic resins as encapsulantsfor FCOB applications may be undesirable, since such applicationstypically require an underfill which is free of solvent and in liquidform during the encapsulation process, and typically require keeping thepackaged system at lower temperatures in order to maintain the integrityof the eutectic solder which is utilized with the organic PWB.

[0012] U.S. Pat. Nos. 6,197,122 and 5,948,922, issued to Ober et al.,disclose thermally reworkable underfill formulations based on thermallydecomposable epoxies containing secondard or tertiary oxycarbonyl(ester) moiety. However, secondard or tertiary oxycarbonyl moietytypically can easily be cleaved by weak acid or base, and is sensitiveto moisture. Also the epoxies containing the secondard or tertiaryoxycarbonyl typically have higher moisture uptake than a standard epoxy.All these facts indicate that epoxies containing secondard or tertiaryoxycarbonyl moiety might not be suitable for underfill application wherehigh reliability is required.

[0013] Thus, it can be seen that none of the prior art methods areideally suited for use as an underfill to bond chip and substrate toallow fast and efficient rework of FCOB devices without sacrificing thereliability of the devices. Therefore, it is desirable to provide anunderfill composition that will not negatively affect the overallperformance of the assembly, while still allowing cost effective andefficient rework.

SUMMARY OF THE INVENTION

[0014] Accordingly, it is an object of this invention to provide apolymeric composition that has properties suited to use as an underfillwhile also offering thermal reworkability. The present invention isfocused on epoxy base materials because epoxy base materials havedesirable properties for use as an underfill and are the only materialsthat have been proven to provide flip-chip devices with acceptablereliability.

[0015] Most epoxy materials are thermosetting compositions and aredifficult or impossible to remove after curing. The present inventionovercomes this limitation by developing new diepoxides that containthermally degradable groups within their structures and using these newdiepoxides in the epoxy formulations to make the thermoset networkdegradable at a desired temperature. This makes the new epoxyformulations reworkable. Moreover, these thermally degradable groupshave good properties such as high moisture resistance, high chemicalresistance and low moisture uptake so that they are suitable forunderfill application. This improvement is advantageous in flip-chipapplication of epoxy compositions where epoxy materials are used as theunderfill to reinforce the solder joints. Removal of the epoxy allowsreplacement of defective devices, saving the cost of discarding othervaluable components in a microelectronic assembly.

[0016] There are two ways of developing reworkable epoxy base materials.One is to develop new epoxies that decompos at rework temperature. Theother is to develop additives to add into the existing epoxyformulations that have previously been found suitable for use asunderfill encapsulants. The present invention focuses on the firstcategory and uses thermally degradable epoxies containing integralthermally cleavable groups that decompose at rework temperatures. Thesecond category is the subject of U.S. Pat. No. 6,172,141.

[0017] The thermally cleavable groups of the present invention have beenselected to meet the following criteria:

[0018] 1. The cleavable groups should be sufficiently stable to permitthe epoxy network to perform its function in a specific application;

[0019] 2. The cleavable groups should be inert to the curing reaction ofthe epoxy network;

[0020] 3. The cleavable groups should not adversely affect the overallproperties of the epoxy network;

[0021] 4. The cleavable groups should decompose quickly at elevatedtemperature so that they break down the structure of the epoxy network,leading to its easy rework.

[0022] 5. The link should be stable in the environment to which thecured epoxy will be exposed.

[0023] 6. The synthesis of the epoxides containing the cleavable linkshould be simple, with high yield, and cost effective.

[0024] The present invention discloses carbonate and carbamate epoxideswhich have been found to meet the above criteria. After introductioninto the epoxy structure, the carbamate and carbonate groups do notsignificantly interfere with epoxy curing, nor do they adversely affectepoxy properties including Tg, modulus, CTE, adhesion. However, theexistence of these groups inside the epoxy structure reduces the epoxydecomposition temperature from 350° C. to as low as 200° C. Optimalrework temperatures for flip-chip devices are generally between 200 and250° C. because the eutectic solder reflow temperature is within thistemperature region. Therefore, these two groups may be suitable for usein applications needing an epoxy which is reworkable around solderreflow temperature.

[0025] More particularly, the present invention is directed to athermally reworkable epoxy composition for encapsulating and protectingan electronic device or assembly. The thermally reworkable epoxycomposition includes the cured reaction product of: a cycloaliphaticepoxide containing either a carbonate or a carbamate group; an organichardener; and a curing accelerator. The present invention is also directto a method of protecting, encapsulating, reinforcing, assembling, orfabricating a device or a chemical product with a cured epoxycomposition which is thermally reworkable, wherein the epoxy compositionincludes the reaction product of: a thermally degradable cycloaliphaticepoxide; an organic hardener; and a curing accelerator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a graph illustrating DCS scan data for Epo0 and Epocarb1through Epocarb4.

[0027]FIG. 2 is a graph illustrating the normalized FT-IR absorbance ofEpocarb2 from room temperature to 250° C. at a heating rate of 10°C./min.

[0028]FIG. 3 is a graph illustrating the normalized FT-IR absorbance ofEpocarb2 from 250° C. to 350° C. at a heating rate of 10° C./min.

[0029]FIG. 4 is a graph illustrating TGA curves for Epo0 and Epocarb1through Epocarb4.

[0030]FIG. 5 is a graph illustrating a Tg-exposure temperature plot forEpocarb1 and Epocarb2.

[0031]FIG. 6 is a graph illustrating the relative adhesion of Epo0 andEpocarb1through Epocarb4.

[0032]FIG. 7 is a graph illustrating Moisture Uptake Data of Epo0,Epocarb1 and Epocarb2.

[0033]FIG. 8 is a graph illustrating DSC cooling curves of Epoxy0 andEpouret1 through Epouret3.

[0034]FIG. 9 is a graph illustrating DSC cooling curves of Epouret4through Epouret7.

[0035]FIG. 10 is a graph illustrating TGA curves of Epoxy0 and Epouret1through Epouret3.

[0036]FIG. 11 is a graph illustrating TGA curves of Epouret4 throughEpouret7.

[0037]FIG. 12 is a temperature profile of a thermocouple on the boardduring chip removal testing.

[0038]FIG. 13 is a schematic of an accessory designed for flip-chiprework.

[0039]FIG. 14 illustrates FT-IR spectra of a clean board and a boardafter cleaning.

DETAILED DESCRIPTION

[0040] The following illustrative embodiments describe the thermallydegradable epoxy underfills of the invention and are provided forillustrative purposes and are not meant as limiting the invention.

[0041] Generally, the reworkable epoxy compositions of the presentinvention include: a cycloaliphatic epoxide containing either carbonateor carbamate group; an organic hardener; and a curing accelerator. Thecompositions of the present invention may also include: a silanecoupling agent; a rubber toughening agent; and/or silica filler. Inaccordance with the exemplary embodiments of the present invention, thecycloaliphatic epoxide used may contain either a carbonate or acarbamate group. The structures of several thermally degradable epoxyresins containing a carbonate group, Carb1 through Carb4, are shownbelow in accordance with the present invention. Among these epoxides,Carb3 is a monoepoxide while all others are diepoxides.

[0042] Likewise, the structures of several thermally degradablediepoxides containing a carbamate (urethane) group, Uret1 through Uret7are illustrated below in accordance with the present invention.

[0043] The properties of several of the compounds are set forth in moredetail in the following sections.

EXAMPLE 1

[0044] This example discloses the synthesis of Carb1.

[0045] 1) Synthesis of di-cyclohex-3-enylmethyl carbonate

[0046] Triphosgene (4.40 g) was dissolved in methylene chloride (80 ml),and added slowly to the methylene chloride solution (200 ml) of3-cyclohexene-1-methanol (9.2 ml), and pyridine (16 ml). The additionwas finished in 1 hr. Then the mixture was kept refluxing for 7 hrs,washed with 0.5 M HCl solution (100 ml), 5% sodium bisulfite (500 ml),2.5% sodium bicarbonate (500 ml), dried with magnesium sulfate, filteredand evaporated to give a 76% yield of liquid product identified by IRand NMR. IR (neat): 3024, 2916, 2839, 1747, 1402, 1259, 962, 751, 656cm⁻¹. ¹H NMR (CDCl₃): δ5.6 (s, 4H, ═CH), 4.0 (d, 4H, CH₂O), 2.2-1.9(complex m, 8H, CH₂), 1.8-1.6 (complex m, 4H, CH₂), 1.4-1.2 (complex m,2H, CH) ppm.

[0047] 2) Synthesis of di-3,4-epoxycyclohexylmethyl carbonate (Carb1)

[0048] Di-cyclohex-3-enylmethyl carbonate (9.80 g) was dissolved inmethylene chloride (75 ml) and acetone (75 ml) in a four-neck flaskequipped with a mechanical stirrer, a pH meter and two adding funnels. ApH 7.5/0.1 M phosphate buffer (50 ml) and an 18-crown-6 crown ether(0.75 g) were then added into the mixture. The mixture was stirred in anice bath to reduce its temperature to below 5° C. before the start ofthe simultaneous addition of a 0.5 M KOH aqueous solution and a solutionof OXONE (potassium peroxymonosulfate, 36.9 g in 200 ml water containing0.05 g of ethylenediaminetetraacetic acid). Rapid stirring was continuedthroughout the addition, and the temperature was kept below 5° C. allthe time. The relative addition speed of the two solutions was adjustedto keep the pH of the reaction mixture in between 7 and 8. Addition ofthe OXONE solution was completed in 2 hrs, followed by additional 3.5hrs of stirring, and the pH was maintained in the above range by a slowaddition of 1.0 M KOH. Then the organic phase was isolated, dried withmagnesium sulfate, filtered and evaporated to give a 90% yield of theliquid diepoxide identified by IR and NMR. IR (neat): 2930, 1744, 1403,1259, 960, 790 cm⁻¹. ¹ H NMR (CDCI₃, in ppm): δ4.0-3.8 (m, 4H, CH₂O),3.1 (d, 4H, CH on epoxide ring), 2.1-0.9 (complex m, 14H, CH₂+CH) ppm.The synthesis scheme for Carb1 is diagrammed below:

EXAMPLE 2

[0049] This example discloses the synthesis of Carb2

[0050] 1) Synthesis of di-1-(3-cyclohexenyl)ethyl carbonate

[0051] The same procedure as of di-cyclohex-3-enylmethyl carbonate wasfollowed except that the alcohol used is 1-(3-cyclohexenyl)-1-ethanolinstead of 3-cyclohexene-1 -methanol. The yield was 80%. Its structurewas identified by IR and NMR. IR (neat): 3024, 2918, 2839, 1739, 1438,1378, 1263, 1141, 1035, 920, 658 cm⁻¹. ¹H NMR (CDCl₃): δ5.6 (s, 4H,═CH), 4.6 (m, 2H, CHO), 2.2-1.9 (complex m, 8H, CH₂), 1.8-1.6 (complexm, 4H, CH₂), 1.4-1.2 (complex, 8H, CH₃+CH) ppm.

[0052] 2)Synthesis of di-1-(3,4-epoxycyclohexenyl)ethyl carbonate(Carb2)

[0053] Following the same epoxidation procedure as for CARB1, a liquidwith 89% yield was obtained which was identified by IR and NMR. IR(neat): 2984, 2938, 1736, 1436, 1363, 1268, 1058, 1030, 927, 794, 736cm⁻¹. ¹H NMR (CDCl₃): δ4.6 (m, 2H, CHO), 3.1 (d, 4H, CH on epoxidering), 2.1-0.9 (complex m, 20H, CH₃+CH₂+CH) ppm.

EXAMPLE3

[0054] This example discloses the synthesis of Carb3.

[0055] 1) Synthesis of cyclohex-3-enylmethyl t-butyl carbonate

[0056] Triphosgene (4.40 g) was dissolved in the methylene chloridesolution (50 ml) and cooled in an ice bath. To this solution a methylenechloride solution (50 ml) of 3-cyclohexene-1-methanol (4.6 ml) andpyridine (8 ml) was slowly added. The addition was finished in 1 hr.Then the mixture was kept stirring for 4 hours in the ice bath duringwhich 3-cyclohexene-1-methyl chloroformate was formed.

[0057] To the above mixture a methylene chloride solution (50 ml) of2-methyl-2-propanol (3.0 ml) and pyridine (8 ml) was then added in oneprotion. The mixture was then stirred at room temperature for overnight.It was washed with 0.5 M HCl solution (100 ml), 5% sodium bisulfite (500ml), 2.5% sodium bicarbonate (500 ml), and dried with magnesium sulfate.The organic phase was then concentrated and purified with columnchromatography on silica gel with methylene chloride to give a 47% yieldof the product as a colorless liquid identified by IR and NMR. IR(neat): 3025, 2918, 2840, 1743, 1396, 1259, 1165, 961, 858, 739, 656cm⁻¹. ¹H NMR (CDCl₃): δ5.6 (s, 2H, ═CH), 4.0-3.8 (d, 2H, CH₂0), 2.2-1.2(complex m, 7H, CH₂+CH), 1.4 (s, 9H, CH₃) ppm.

[0058] 2) Synthesis of 3,4-epoxycyclohexylmethyl t-butyl carbonate(Carb3)

[0059] Following the same epoxidation procedure as for Carbl, a liquidwith 89% yield was obtained which was identified by IR and NMR. IR(neat): 2982, 2933, 1743, 1255, 1163, 859, 790 cmn⁻¹. ¹H NMR (CDCl₃):δ4.0-3.8 (m, 2H, CH₂O), 3.2 (d, 2H, CH on epoxide ring), 2.2-1.0(complex m, 7H, CH₂+CH), 1.4 (s, 9H, CH₃) ppm. The synthesis scheme forCarb3 is diagrammed below:

EXAMPLE 4

[0060] This example discloses the synthesis of Carb4.

[0061] 1) Synthesis of 4-vinylphenyl2-(3-methyl-3-cyclohexenyl)-2-propyl carbonate

[0062] In a 250 ml three-necked round-bottomed flask equipped with adropping funnel, a nitrogen bubblier and a magnetic stirring bar,triphosgene (1.0 g) in methylene chloride solution (50 ml) was placed.The temperature was lowed to 0° C. with ice bath. A methylene chloridesolution (50 ml) of 4-vinyl phenol (1.2 g) and pyridine (8 ml) was addeddropwise over 30 min from the dropping funnel. The resulting mixture wasstirred at 0-5° C. for 8 hr and the reaction proceeding was monitoredwith TLC till all 4-vinyl phenol was converted to 4-vinylphenylchlorofornate.

[0063] The resulting mixture above was used directly without treatmentand the same reaction system was used continuously. The dropping fumnelon the flask was charged of α-terpineol (7.7 g) and quinoline (6.5 g).The formed solution was added dropwise to the reaction system at roomtemperature over vigorous stirring. The mixture was stirred over nightand a white salt gradually precipitated. The salt was separated and theorganic phase was washed with 2 N HCl and water until all pyridine andquinoline were neutralized and washed out. The organic phase wasseparated, washed with sodium bicarbonate and sodium bisulfite solution,and then dried over anhydrous magnesium sulfate. The columnchromatography of the products on silica gel with 10:1 hexane/ethylacetate gave 32% yield of the product as a colorless viscous liquid.FT-IR (neat): 2925, 1757, 1508, 1446, 1376, 1264, 1214, 1157, 1123,1018, 990, 903, 840, 809 cm⁻¹. ¹H NMR (CDCl₃): δ7.40 (d, 2H, aromatic),7.12 (d, 2H, aromatic), 6.69 (dd, 1H, ═CH, aromatic), 5.70 (dd, 1H,═CH2), 5.38 (m, 1H, ═CH), 5.24 (dd, 1H, ═CH2), 2.19-1.83 (m, 6H, C11₂),1.66 (s, 3H, CH₃) 1.54 (s, 3H, CH₃), 1.51 (s, 3H, CH₃), 1.44-1.25 (m,1H, CH) ppm.

[0064] 2) Synthesis of 4-epoxyethyllphenyl2-(3-methyl-3,4-epoxycyclohexy1)-2-propyl carbonate (Carb4)

[0065] Following the same epoxidation procedure as for Carb1, a viscouscolorless liquid with 89% yield was obtained. FT-IR (neat): 2925, 1757,1508, 1446, 1376, 1264, 1214, 1157, 1123, 1018, 990, 903, 840, 809 cm⁻¹.¹H NMR (CDCl₃): δ7.40 (d, 2H, aromatic), 7.11 (d, 2H, aromatic), 3.70(dd, 1H, CO), 3.14 (t, 1H, CO), 2.89 (d, 1H, CHO), 2.81 (d, 1H, CHO),2.12-1.44 (m, 6H, CH₂), 1.62 (s, 3H, 1CH₃), 1.52 (s, 3H, 1CH₃), 1.50 (s,6H, 2CH₃), 1.42-1.20 (m, 1H, CH) ppm. The synthesis scheme for Carb4 isdiagrammed below:

EXAMPLE 5

[0066] This example discloses Epoxide Equivalent Weights (EEWs) of Carblthrough Carb4.

[0067] Their EEWs were measured according to ASTM titration procedureD1652-90. Table 1 shows their theoretical and measured EEW values. Itcan be seen that the measured values were generally in good agreementwith the theoretical values. TABLE 1 EEWs of Carb1 through Carb4 EEW(g/mol.) Sample Theoretical Measured Carb1 141 157 Carb2 153 165 Carb3228 235 Carb4 165.5 207

EXAMPLE 6

[0068] This example discloses the synthesis of Uret1.

[0069] 1) Synthesis of 3-cyclohexene-1-isocyanate

[0070] Sodium azide (8.00 g) was dissolved in water (20 ml) in a 250 ml3-neck flask. The flask was put in an ice path to control thetemperature around 0° C. While the aqueous solution was stirred, benzenesolution (100 ml) of 3-cyclohexene-1-carbonyl chloride (8.70 g) wasadded in dropwise. The addition was completed in about 2 hrs. Themixture was stirred for another 4 hrs, with the temperature around 0° C.Then the aqueous phase was separated from the organic phase, extractedwith benzene (50 ml). The two organic phases were combined and driedwith magnesium sulfate for several hours. The dried benzene solution wasthen heated to 50° C. in a 250 ml flask in a water bath for severalhours until no gas was emitted. The obtained benzene solution ofisocyanate was directly used for later synthesis.

[0071] 2) Synthesis of 3-cyclohexen-1-isocyanate cyclohex-3-enylmethylcarbamate

[0072] A Benzene solution of isocyanate (65 ml),3-cyclohexene-l1-methanol (3.50 ml), and pyridine (3.00 ml) were mixedin a 250 ml 3-neck flask, refluxing for 6 hrs. Then water (100 ml) wasadded in. The mixture was refluxed for another 1 hr. The mixture wasthen washed with 0.05 M HCl three times, followed by water three times.The organic phase was then separated from the water phase and dried withmagnesium sulfate for several hours before benzene was removed by rotaryevaporation to give a liquid. It was purfed by column chromatographywith 60% yield. This liquid material was identified by its spectra. IR(neat, in cm⁻¹n): 3340, 3025, 2915, 2845, 2255, 1700, 1525, 1440, 1305,1270, 1235, 1140, 1050, 975, 925, 875, 780, 750, 720, 655. ¹H NMR(CDCl₃, in ppm): δ7.1 (d, m, 1H), 5.7-5.5 (d, s, 4H), 3.8 (d, s, 2H),3.5 (s, m, 1H), 3.3 (d, s, 2H), 2.2-1.6 (complex, s, 9H), 1.5-1.1(complex, m, 2H). Its purity was verified by TLC.

[0073] 3) Synthesis of 3,4-epoxycyclohexyl-1-isocyanate3,4-epoxycyclohexylmethyl carbamate (Uret1)

[0074] 3-cyclohexen-1-isocyanate cyclohex-3-enylmethyl carbamate (9.80g) was dissolved in methylene chloride (75 ml) and acetone (75 ml) in afour-neck flask equipped with a mechanical stirrer, a pH meter and twoadding funnels. A pH 7.5/0.1 M phosphate buffer (50 ml) and an18-crown-6 crown ether (0.75 g) were then added into the mixture. Themixture was stirred in an ice bath to reduce its temperature to below 5°C. before the start of the simultaneous addition of a 0.5 M KOH aqueoussolution and a solution of OXONE (potassium peroxymonosulfate, 36.9 g in200 ml water containing 0.05 g of ethylenediaminetetraacetic acid).Rapid stirring was continued throughout the addition, and thetemperature was kept below 5° C. all the time. The relative additionspeed of the two solutions was adjusted to keep the pH of the reactionmixture in between 7 and 8. Addition of the OXONE solution was completedin 2 hrs, followed by additional 3.5 hrs of stirring, and the pH wasmaintained in the above range by a slow addition of 1.0 M KOH. Then theorganic phase was isolated, dried with magnesium sulfate, filtered andevaporated to give a 92% yield of the liquid diepoxide identified by IRand NMR. IR (neat, in cmn⁻¹): 3340, 2940, 1700, 1530, 1435, 1310, 1255,1225, 1045, 800. ¹H NMR (CDCl₃, in ppm): δ5.0 (d, m, 1H), 4.6 (s, m,1H), 3.8 (m, m, 2H), 3.6 (s, m, 1H), 3.2-3.0 (m, s, 4H), 2.4-0.9(complex, 12H).

[0075] The synthesis scheme for Uret1 is diagrammed below:

EXAMPLE 7

[0076] This example discloses the synthesis of Uret2.

[0077] 1) Synthesis of 3-cyclohexen-1-isocyanate2-(3-cyclohexenyl)-2-propyl carbamate

[0078] 3-cyclohexen- 1-isocyanate 2-(3-cyclohexenyl)-2-propyl carbamatewas obtained by following the same procedure as for 3-cyclohexen-1-isocyanate cyclohex-3 -enylmethyl carbamate except2-(3-cyclohexenyl)-2-propanol was used to replace3-cyclohexen-1-methanol. It was purified by column chromatography with44% yield. Spectra confirmed the structure. IR (neat, in cm⁻¹): 3333,3025, 2928, 2825, 1620, 1531, 1438, 650. ¹H NMR (CDCl₃, in ppm):δ5.7-5.5 (d, s, 411), 3.7 (s, m, 111), 2.4-1.3 (complex, 14H), 1.2 (m,s, 6H). Its purity was verified by TLC.

[0079] 2) Synthesis of 3,4-epoxycyclohexyl-1-isocyanate 2-(3,4-epoxycyclohexyl)-2-propyl carbamate (Uret2)

[0080] Following the same procedure as for Uret1, a 95% yield of Uret2was obtained and identified by IR and NMR. IR (neat, in cm⁻¹): 3345,2974, 2925, 1700, 1525, 1358, 802. ¹H NMR (CDCl₃, in ppm): δ3.6 (s, m,1H), 3.3-3.0 (d, s, 4H), 2.4-1.3 (complex, 14H), 1.2 (m, s, 6H).

EXAMPLE 8

[0081] This example discloses the synthesis of Uret3.

[0082] 1) Synthesis of cyclohex-3-enylmethyl chloroformate2-(I-cyclohexenyl) ethyl carbamate

[0083] To the methylene chloride solution (40 ml) of triphosgene (2.20g), a methylene chloride solution (60 ml) of 3-cyclohexen-1-methanol(2.40 ml) and pyridine (3.50 ml) was slowly added. The addition wascompleted in 1 hr. The mixture was then refluxed for 1 hour, cooled downto room temperature, and stirred for another 2 hrs. A yellowish greensolution was obtained.

[0084] Methylene chloride solution (50 ml) of 2-(1-cyclohexenyl)ethylamine (2.70 ml) and pyridine (3.50 ml) was added into the abovementioned yellowish green solution in one portion. Instantly, the colorof the mixture changed from yellowish green to pink. The mixture wasrefluxed for 2 hrs. Then it was washed with 0.5M HCl, water, 5% sodiumbisulfite solution, 2.5% sodium bicarbonate solution, and saturatedsodium chloride solution before it was dried with magnesium sulfate,filtered, and evaporated to give a 80% yield of liquid. Its structurewas confirmed by the IR and NMR spectra. IR (neat, in cm⁻¹): 3403, 3341,3019, 3017, 2845, 1718, 1515, 1439, 1254, 742, 653. ¹H NMR (CDCl₃, inppm): δ5.6 (t, s, 2H), 5.5-5.3 (m, m, 1H), 4.0(m, m, 2H), 3.5 (d, s,2H), 3.3 (d, m, 1H), 2.2-1.2 (complex, 17H). Its purity was verified byTLC.

[0085] 1) Synthesis of 3,4-epoxycyclohexylmethyl2-(1,2-epoxycyclohexyl)ethyl carbamate (Uret3)

[0086] Following the same procedure as for Uret1, an 89% yield of Uret3in the form of a liquid was obtained and identified by IR and NMR. IR(neat, in cm⁻¹): 3345, 2932, 1708, 1520, 1436, 1252, 735.11¹H NMR(CDCl₃, in ppm): δ5.1 (s, w, 1H), 3.9-3.7 (m, m, 2H), 3.4-2.9 (complex,6H), 2.2-0.9 (complex, 16H). The synthesis scheme for Uret3 isdiagrammed below:

EXAMPLE 9

[0087] This example discloses the synthesis of Uret4.

[0088] 1) Synthesis of Phenylene-1,4-diisocyanateBis-(cyclohex-3-enylmethyl) dicarbamate

[0089] To a pyridine solution (40 ml) of 3-cyclohexene-1-methanol (12.00ml) in the 500 ml 3-neck flask equipped with a temperature controller, acondenser, and an adding funnel, an acetone solution (150 ml) ofphenylene-1,4-diisocyanate (12.00 g) was slowly added in, while themixture was kept stirring. The addition was completed in 1 hr, followedby refluxing for 6 hrs. Then acetone and pyridine were evaporated out togive a raw solid product with 79% yield. The raw solid was washed with0.5 M HCl and water several times, before it was dried in vacuum.Spectra confirmed the structure. IR (KBr pellet, in cm⁻¹): 3329, 3025,2948, 2850, 1700, 1539, 1413, 1304, 1239, 1067, 649. ¹H NMR (CDCl₃, inppm): δ7.3 (s, s, 4H), 6.7 (s, m, 2H), 5.7 (s, s, 4H), 4.0 (d, s, 4H),2.2-1.2 (complex, 14H). Its purity was verified by TLC.

[0090] 2) Synthesis of Phenylene-1,4-diisocyanateBis-(3,4-epoxycyclohexylmethyl) dicarbamate (Uret4)

[0091] Following the same procedure as for Uret1, solid Uret4 with yield81% was obtained and identified by IR and NMR. IR (KBr pellet, in cm⁻¹):3330, 2943, 1702, 1542, 1423, 1305, 1228, 1069, 817, 853. ¹H NMR (CDCl₃,in ppm): δ7.3 (s, s, 4H), 6.5 (s, m, 2H), 3.9 (m, s, 4H), 3.2 (d, s,4H), 2.2-1.0 (complex, 14H).

EXAMPLE 10

[0092] This example discloses the synthesis of Uret5.

[0093] 1) Synthesis of Tolylene-2,4-diisocyanateBis-(cyclohex-3-enylmethyl) dicarbamate

[0094] Following the same procedure as for phenylene-1,4-diisocyanatebis-(cyclohex-3-enylmethyl) dicarbamate except that an acetone solutionof phenylene-1,4-diisocyanate was replaced by tolylene-2,4-diisocyanate,solid tolylene-2,4-diisocyanate bis-(cyclohex-3-enylmethyl) dicarbamatewas obtained with 78% yield, and was identified by IR and NMR. IR (KBrpellet, in cm⁻¹): 3329, 3015, 2900, 2813, 1702, 1542, 1413, 1304, 1230,1067, 649. ¹H NMR (CDCl₃, in ppm): δ7.2-7.0 (complex, 3H), 6.6-6.4 (d,m, 2H), 5.6 (s, s, 4H), 4.0 (m, s, 4H), 2.3-1.2 (complex, 17H). Itspurity was verified by TLC.

[0095] 2) Synthesis of Tolylene-2, 4-diisocyanate Bis-(3,4-epoxycyclohexylmethyl) dicarbamate (Uret5)

[0096] Following the same procedure as for Uret1, solid Uret5 with yield85% was obtained and identified by IR and NMR. IR (KBr pellet, in cm⁻¹):3303, 2936, 1730, 1599, 1532, 1416, 1224, 1056. 1¹H NMR (CDCl₃, in ppm):δ7.2-7.0 (complex, 3H), 6.6-6.4 (d, m, 2H), 3.9 (m, s, 4H), 3.1 (s, s,4H), 2.3-1.2 (complex, 17H).

EXAMPLE 11

[0097] This example discloses the synthesis of Uret6.

[0098] 1) Synthesis of Isophorone diisocyanateBis-(cyclohex-3-enylmethyl) dicarbamate

[0099] Isophorone diisocyanate bis-(cyclohex-3-enylmethyl) dicarbamatesolid was obtained with 80% yield by following the same procedure as forphenylene-1,4-diisocyanate bis-(cyclohex-3-enylmethyl) dicarbamateexcept that the acetone solution of phenylene-1,4-25 diisocyanate wasreplaced by isophorone diisocyanate. IR and NMR spectra confirmed thestructure. IR (KBr pellet, in cm⁻¹): 3343, 3025, 2938, 1684, 1529, 1257,1222, 1140, 643. 1¹H NMR (CDCl₃, in ppm): δ5.6 (s, s, 4H), 4.6 (s, m,2H), 3.9 (d, s, 4H), 3.1 (s, s, 3H), 2.1-1.2 (complex, 29H). Its puritywas verified by TLC.

[0100] 2) Synthesis of Isophorone diisocyanateBis-(3,4-epoxycyclohexylmethyl) dicarbamate (Uret6)

[0101] Uret6 solid was obtained with 90% yield by following the sameprocedure as for Uret1. Its structure was identified by IR and NMR. IR(KBr pellet, in cm⁻¹): 3344, 2937, 1683, 1531, 1257, 1140, 1050. ¹H NMR(CDCl₃, in ppm): δ4.6 (s, m, 2H), 3.8 (m, s, 4H), 3.1 (s, s, 7H),2.1-1.2 (complex, 29H).

EXAMPLE 12

[0102] This example discloses the synthesis of Uret7.

[0103] 1) Synthesis of Hexylene-1,6-diisocyanateBis-(cyclohex-3-enylmethyl) dicarbamate

[0104] Following the same procedure as for phenylene-1,4-diisocyanatebis-(cyclohex-3-enylmethyl) dicarbamate except that the acetone solutionof phenylene-1,4-diisocyanate was replaced by hexylene-1,6-diisocyanate, hexylene- 1,6-diisocyanate bis-(cyclohex-3-enylmethyl)dicarbamate, in the form of a semi-solid, was obtained with 87% yield,and was identified by IR and NMR. IR (neat, in cm⁻¹): 3328, 2925, 2840,1701, 1542, 1355, 1024, 780, 653. ¹H NMR (CDCl₃, in ppm): δ5.6 (s, s,4H), 4.7-4.4 (d, w, 2H), 3.9 (d, s, 4H), 2.9 (d, m, 2H), 2.1-0.8(complex, 24H). Its purity was verified by TLC.

[0105] 2) Synthesis of Hexylene-1,6-diisocyanateBis-(3,4-epoxycyclohexylmethyl) dicarbamate (Uret7)

[0106] A Semi-solid Uret7 was obtained with 88% yield by following thesame procedure as for Uret1l. Its structure was identified by IR andNMR. IR (neat, in cm⁻¹): 3347, 2918, 1704, 1532, 1309, 1247, 1146, 1041,792. ¹H NMR (CDCl₃, in ppm): δ4.7-4.4 (d, w, 2H), 3.8 (d, S 4H), 3.1 (d,s, 4H), 2.9 (d, m, 2H), 2.1-0.8 (complex, 24H). The synthesis scheme forUret4 through Uret7 is diagrammed below:

EXAMPLE 13

[0107] This example discloses Epoxide Equivalent Weights (EEWs) of Uret1through Uret7.

[0108] The Epoxide Equivalent Weights (EEWs) of these diepoxides weremeasured according to ASTM titration procedure Dl1652-90. Table 2 showstheir theoretical and measured EEW values. It can be seen that themeasured values are in good agreement with the theoretical values. TABLE2 EEWs of Uret1 though Uret7 EEW (g/mol.) Sample Theoretical MeasuredUret1 133.5 141 Uret2 147.5 164 Uret3 147.5 186 Uret4 208 222 Uret5 215284 Uret6 212 232 Uret7 239 268

EXAMPLE 14

[0109] This example discloses structure of other chemicals used in thestudy.

[0110] Table 3 lists the chemical structures of a commercial epoxyresin, hardener and catalyst used in the experiments. The commercialepoxy resin, 3,4-epoxy cyclohexyl methyl-3,4-epoxy cyclohexylcarboxylate, was provided by Union Carbide under the Trade Name ERL4221and used as received. Its Epoxide Equivalent Weight (EEW) is 133 g/mol.The hardener, hexahydro-4-methylphthalic anhydride (HHMPA), waspurchased from Aldrich Chemical Company, Inc. and used as received. Thecatalyst, imidazole, was also purchased from Aldrich Chemical Company,Inc. and used as received.

[0111] One of ordinary skill in the art will recognize that a number ofother compounds may be suitable for use with the cycloaliphatic epoxiesof the present invention. For example, and not limitation, the organichardener may also comprise any organic carboxylic acid anhydridehardener and in particular: hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl-5-norbomene-2,3-dicarboxylicanhydride, tetrahydrophthalic anhydride, methyl tetrahydrophthalicanhydride, and nadic methyl anhydride. Other curing accelerators whichmay be suitable for use in accordance with the present inventioninclude: triphenylphosphine, 2-ethyl-4-methyl imidazole,1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, imidazole,1-methylimidazole, 1-benylimidazole, 1,2-dimethylimidazole,1-benzyl-2-methylimidazole, 4-methyl-2-phenylimidazole,benzyldimethylamine, triethylamine, pyridine, dimethylaminopyridine,1,4-diazabicyclo[2.2.2.]octane, 1,8-diazabicyclo[5.4.0]undec-7-ene, and1,5-diazabicyclo[4.3.0]non-5-ene. Finally, the filler may selected fromsilica fillers with a variety of different particle sizes and particlesize distributions. TABLE 3 Chemical Ingredients Used for ReworkableEpoxy Sample Preparation Name of chemicals Structure of ChemicalsERL4221

HHMPA

Imidazole

EXAMPLE 15

[0112] An electromagnetic stirrer was used to mix the epoxy resin,hardener, and catalyst. The four synthesized diepoxides were mixed withHHMPA, respectively, in a mole ratio 1:0.8 and 1% in weight of catalystimidazole, and were called Epocarbi through Bpocarb4. ERL422l was alsomixed with HHMPA and imidazole in the same ratio and was called Epo0(see Table 4). The mixture was stirred until a homogeneous phase wasformed. TABLE 4 Composition of Epo0 and Epocarb1 Through Epocarb4Epoxide/Anhydride Catalyst Sample (1/0.8 mol) (1 wt %) Epo0ERL4221/HHMPA Imidazole Epocarb1 Carb1/HHMPA Imidazole Epocarb2Carb2/HHMPA Imidazole Epocarb3 Carb3/HHMPA Imidazole Epocarb4Carb4/HHMPA Imidazole

EXAMPLE 16

[0113] It was found that carbonate linkage inside the epoxide structuredid not react with epoxy composition and was inert to epoxy curing dueto the fact that carbonate linkage was a fairly chemically stable group.FIG. 1 shows the curing profiles of four formulations based on thesefour epoxides as compared to Epo0. It can be seen that they all curedsimilarly compared to Epo0. Endothermic peaks for Epocarb3 and Epocarb4around 200° C. were caused by decomposition.

EXAMPLE 17

[0114] Time-resolved FT-IR proved to be a useful tool to monitor thecuring and degradation of epoxy system. IR spectra of Epocarb4 werecollected at different temperatures at a heating rate of 10° C./min andanalyzed. The curing process was easily monitored by a decrease inabsorbance at 1864 and 1789 cm⁻¹ (HHMPA anhydride C═O stretching) and at901 cm⁻¹ (epoxide C—O—C ring deformation). Furthermore, the increase ofthe absorbance at 1155 cm⁻¹ (ester C—O stretching) and 1736 cm⁻¹ (esterC═O stretching) is the clear sign of ester formation during theepoxy-anhydride curing. The absorbance at 1266 cm⁻¹ (carbonate C—Ostretching) was used as an internal standard to normalize the baselineand film thickness change of the sample during reaction. FIG. 2 showsthe normalized FT-IR absorbance of Epocarb2 from room temperature to250° C.

EXAMPLE 18

[0115] Degradation of Epocarb2 was studied by analyzing its IR spectrafrom 250° C to 350° C. While the absorbance at 1736 and 1155 cm⁻¹decreased slightly which was probably caused by the film thicknesschange, the absorbance at 1266 cm⁻¹ decreased much faster. FIG. 3 showsthe normalized FT-IR absorbance (by 1155 cm⁻¹ ) of Epocarb2 from 250° C.to 350° C. The decrease of 1266 cm⁻¹ was caused by the thermal cleavageof carbonate linkage, which is the mechanism for Epocarb2 degradation.Other samples were also studied by time-resolved FT-IR and similarresults were obtained.

EXAMPLE 19

[0116]FIG. 4 shows the TGA curves of the cured samples at a heating rateof 10° C./min. It is clear that all these samples based oncarbonate-containing epoxides degraded at lower temperature than thatbased on ERL4221. In addition, it can be drawn from the figure thatthermal stability of these epoxides in very general terms goes in thefollowing order: tertiary carbonate<secondary carbonate<primarycarbonate.

EXAMPLE 20

[0117] Degradation kinetics of epoxy can be described by the followingequation:

1n R=1n (dα/dt)=F+1n A −E/RT

[0118] where R is reaction rate, a is conversion, t is time, F is aconstant, A is the pre-exponential factor and E is activation energy.Degradation kinetics of Epo0, Epocarb1 and Epocarb2 was studied by usingTGA at four different heating rates. At different degree of conversionand temperature, the degradation kinetics may be different and can beinfluenced by many factors including sample shape, volatility, localatmosphere and thermal transfer. So all samples were tested under thesame TGA conditions. The activation energy of the thermal decompositionas calculated above (see Table 5) is the average activation energy atlow conversion, α=0.01-0.10, which is due to the initial decompositionof the weak linkages. Epo0 (primary ester linkage) had higher activationenergy than Epocarb1 (primary carbonate linkage), and Epocarb1 hadhigher activation energy than Epocarb2 (secondary carbonate linkage). Itcan be seen that these calculated activation energy results are in goodaccordance with the onset decomposition temperatures of these threematerials. TABLE 5 Thermal Decomposition Activation Energies of Epo0,Epocarb1 and Epocarb2 Calculated from TGA Kinetics Sample ActivationEnergy E_(a) (kJ/mol) Epo0 152.7 Epocarb1 124.8 Epocarb2 112.3

EXAMPLE 21

[0119] TGA results show that Epocarb1 and Epocarb2 started weight lossaround 250° C., which is much higher than the targeted reworktemperature, 220° C. However, TGA is not a very good tool to determinenetwork break-down temperature because it can only measure weight lossvs. temperature, but the network may have already partially broken downeven though the products are not volatile enough to produce anydetectable mass change. Therefore, it was decided to use Tg change ofthe epoxy network to represent the network break-down. First, tenspecimens of each epoxy formulation were prepared by curing at 175° C.for 30 minutes. Among these specimens, nine were then exposed todifferent temperatures by staying in a preheated oven for 5 minutes. Thetemperature ranged from 200 to 280° C. for every 10° C. increment. Thenthe Tgs of these nine high temperature treated specimens and thenon-treated specimen were determined by DSC. FIG. 5 shows the Tg vs.exposure temperature curve for Epocarb1 and Epocarb2. It shows that bothformulations had network-break down temperature around 220° C., which isjust the temperature we need. It also shows that Epocarb2 had networkbreak-down much faster than Epocarb1, which can be explained by the lessthermal stability of secondary carbonate linkage than primary carbonatelinkage.

EXAMPLE 22

[0120] Various properties of Epocarb1 and Epocarb2 were measured andcompared to those of Epo0. Table 6 lists the Tg, CTE, Storage Modulus,and room temperature viscosity of Epocarb1 and Epocarb2 as compared toEpo0. It is clear that both EpocarbI and Epocarb2 were comparable toEpo0 in any of these categories. TABLE 6 Properties of Epo0, Epocarb1,and Epocarb2 Sample Epo0 Epocarb1 Epocarb2 Tg (° C.) 175 176 176 CTE(ppm/° C., 50-100° C.) 75 76 85 Storage Modulus (GPa, at 25° C.) 2.6 2.82.5 Viscosity (Pa.S, At 25° C.) 0.24 0.30 0.34

EXAMPLE 23

[0121] The adhesion of Epocarb1 and Epocarb2 was also studied. FIG. 6shows the adhesion data of Epocarb1, Epocarb2 and Epo0, which shows bothEpocarb1and Epocarb2 had comparable adhesion compared to Epo0.

EXAMPLE 24

[0122] Moisture uptake of Epocarb1 and Epocarb2 was measured andcompared to that of Epo0. FIG. 7 shows the results from moisture uptakemeasurements. The moisture uptake of Epocarb1 and Epocarb2 was lowerthan Epo0, which can be explained by the less hydrophilicity ofcarbonate group than ester group. The fact that Epocarb2 picked up lessmoisture than Epocarb 1 could be explained by the less hydrophilicity ofCarb2 than Carb1 with the additional methyl group.

EXAMPLE 25

[0123] This example discloses the chemicals and formulations used tostudy Uret1 through Uret7.

[0124] ERL4221 was used as the epoxy resin while HHMPA was used as thehardener. The catalyst, 1-cyanoethyl-2-ethyl-4-methylimidazole (EMZCN),was provided by Shikoku company and used as received.

[0125] An electromagnetic stirrer was used to mix the epoxy resin,hardener, and catalyst. The seven synthesized diepoxides were mixed withHHMPA, respectively, in a mole ratio 1:0.8 and 4 wt % of catalyst EMZCN,and were called Epouretl through Epouret7. ERL4221 was also mixed withHHMPA and EMZCN in the same ratio and was called Epoxy0 (see Table 7).The mixture was stirred until a homogeneous phase was formed. TABLE 7Composition of Epoxy0 and Epouret1 Through Epouret7 Epoxide/AnhydrideCatalyst Sample (1/0.8 mol) (4 wt %) Epoxy0 ERL4221/HHMPA EMZCN Epouret1Uret1/HHMPA EMZCN Epouret2 Uret2/HHMPA EMZCN Epouret3 Uret3/HHMPA EMZCNEpouret4 Uret4/HHMPA EMZCN Epouret5 Uret5/HHMPA EMZCN Epouret6Uret6/HHMPA EMZCN Epouret7 Uret7/HHMPA EMZCN

EXAMPLE 26

[0126]FIG. 8 shows the curing profiles of formulations Epoxy0 throughEpouret3. FIG. 9 shows the curing profiles of Epouret4 through Epouret7.It is clear that Epoxy0 cured at a higher temperature region than theother formulations. This indicated that there might be some interactionsbetween the carbamate linkage and epoxy curing, causing the peak ofepoxy curing to shift to a lower temperature region.

EXAMPLE 27

[0127]FIG. 10 shows the TGA curves of cured samples Epoxy0 throughEpouret3. It clearly shows that the sample from ERL4221 was quitethermally stable. It did not start losing weight until after 350° C. Forthe three cured samples from liquid formulations, Epouret1 throughEpouret3, decomposition started at much lower temperatures. By comparingthe curve of Epouret1, which showed its onset decomposition temperaturearound 280° C., to the curve of Epouret2, which showed its onsetdecomposition temperature around 220° C., it is clear that the carbamategroup from a tertiary alcohol degraded at a much lower temperature thanthe one from a primary alcohol.

[0128]FIG. 11 shows the TGA curves of the formulations from the foursolid diepoxides, Epouret4 through Epouret7. The formulations usingsolid diepoxides started to decompose at temperatures below 300° C.Moreover, the two formulations from Uret6 and Uret7—Epouret6 andEpouret7—had higher onset decomposition temperatures than Epouret4 andEpouret5.

EXAMPLE 28

[0129] This example discloses the composition of a thermally reworkableunderfill formulation based on Carb1 as shown in Table 8. Thisformulation is named GT-1″. TABLE 8 Composition of GT-1″ Epoxide/Anhydride Imidazole Filler Silane Tougher Sample (1/0.8 mol) (1 wt %)Loading (1 wt %) (10 mole %) GT-1″ Carb1/HHMPA Y 50% Y Y

EXAMPLE 29

[0130] This example discloses a developed rework process.

[0131] Chip Removal

[0132] Chip removal test was conducted on the rework station usingassembled and underfilled flip chip test boards. Temperature profile ofthe board site during chip removal was obtained by monitoring the actualtemperature inside the board during chip removal through a buriedthermal couple. Through adjusting various machine parameters andchecking the subsequent temperature profiles of the board site, a chipremoval profile allowing the board site to reach desired reworktemperature without damaging the board was obtained. This chip removalprofile was found to loosen the reworkable underfill at peaktemperature. The major steps of the profile is listed as follows:

[0133] 1. Preheat

[0134] Top and bottom heater was set at 200° C. The board was heateduntil 25 seconds had passed since the preset temperature was reached.

[0135] 2. Activate

[0136] Top and bottom heater was set at 270° C. The board was heateduntil 20 seconds had passed since the preset temperature was reached.

[0137] 3. Adjust Head Position

[0138] 4. Reflow

[0139] Top heater was set at 380° C. while the bottom heater was set to400° C. The board was heated until 30 seconds had passed since thepreset temperature was reached.

[0140] 5. Remove Part

[0141]FIG. 12 shows the temperature profile of the board using theestablished chip removal profile.

[0142] By using this rework profile, non-underfilled chips were found tobe easily removed by the vacuum force applied through the nozzle.However, the nozzle could not remove the underfilled chips from theboard because the vacuum force was not strong enough. An accessory wasthen designed, manufactured, and mounted onto the small nozzle for flipchip rework. The schematic of this design is shown in FIG. 13. The ideawas to have the accessory holding the chip during the rework. This wouldallow shear or twisting force to be applied to the chip.

[0143] This accessory was put to test. After the nozzle touched thechip, the frame that held the board was slowly moved in both X and Ydirections in order to apply a shear force on the chip. This was foundto not only apply the shear force to the chip, but also help remove partof the underfill fillet, which helped the subsequent site-cleaning stepas the underfill fillet was the most difficult part to remove. Afterthat, the chip was lifted up by the nozzle and removed from the board.

[0144] Site-Cleaning

[0145] After chip removal, the underfill residue and solder residue hadto be cleaned and the site prepared to accept a new chip. Differentcleaning methods were tried and the combination of a gentle mechanicalprocess with solvent cleaning worked best. The mechanical cleaning wasdone by using a horsehair brush which was attached to a Dremel tool toslowly and carefully sweep away the underfill residue. The debrisgenerated during the mechanical cleaning was then removed by isopropylalcohol (IPA). This cleaning method was found to clean the underfillresidue and the solder residue simultaneously with minimum damage to thesolder mask and bump pads on the FR-4 board. FIG. 14 shows thecomparison of the IR spectrum of a board after clean vs. a clean board.Both spectra matched well, indicating that the board was clean after thecleaning step.

[0146] Chip Replacement

[0147] New chips were assembled on the reworked sites following the sameprocedure for test vehicle assembly. Inspecting replaced chips usingcontinuity test and x-ray machine found that good solder interconnectswere formed. High yield chip replacement was achieved on the replacedchips, which indicated that the cleaning process maintained theintegrity of the bond pads.

EXAMPLE 30

[0148] This example discloses the rework test results of GT-1″. Flipchips underfilled with GT-1″ could be reworked using the above reworkprocess. Underfill and solder residue were removed during the cleaningprocess. The bond pads at the rework site kept their integrity. Newchips were placed on the reworked sites and good electrical continuitywas achieved.

EXAMPLE 31

[0149] This example discloses a reliability test for GT- 1″.

[0150] Reliability of underfilled flip chips was measured by subjectingthe boards to liquid-to-liquid thermal shock (LLTS) test using an ESPECThermal Shock Chamber. The test condition was 10-minute cycle from −55to 125° C., with 5 minutes cold and 5 minutes hot.

EXAMPLE 32

[0151] This example discloses reliability test results for GT-1″.Average number of cycles a flip chip underfilled with GT-1″ couldwithstand is 1500 cycles, which is comparable to a high performancecommercial non-reworkable underfill.

What is claimed is:
 1. A thermally reworkable epoxy composition forencapsulating and protecting an electronic device or assembly, saidcomposition comprising the cured reaction product of: a cycloaliphaticepoxide containing either a carbonate or a carbamate group; an organichardener; and a curing accelerator.
 2. The epoxy composition of claim 1,wherein said cycloaliphatic epoxide contains an aliphatic carbonategroup.
 3. The epoxy composition of claim 2, wherein said cycloaliphaticepoxide is di-3,4-epoxycyclohexylmethyl carbonate.
 4. The epoxycomposition of claim 2, wherein said cycloaliphatic epoxide isdi-1-(3,4-epoxycyclohexenyl)ethyl carbonate.
 5. The epoxy composition ofclaim 2, wherein said cycloaliphatic epoxide is3,4-epoxycyclohexylmethyl t-butyl carbonate.
 6. The epoxy composition ofclaim 2, wherein said cycloaliphatic epoxide is 4-epoxyethyllphenyl2-(3-methyl-3,4-epoxycyclohexyl)-2-propyl carbonate.
 7. The epoxycomposition of claim 1, wherein said cycloaliphatic epoxide contains acarbamate group.
 8. The epoxy composition of claim 7, wherein saidcycloaliphatic epoxide is selected from the group consisting of,3,4-epoxycyclohexyl-1-isocyanate 3,4-epoxycyclohexylmethyl carbamate;3,4-opoxycyclohexyl-1-isocyanate 2-(3 ,4-epoxycyclohexyl)-2-propylcarbamate; 3,4-epoxycyclohexylmethyl 2-( 1,2-epoxycyclohexyl)ethylcarbamate; phenylene-1,4-diisocyanate Bis-(3,4-epoxycyclohexylmethyl)dicarbamate; tolylene-2,4-diisocyanate Bis-(3,4-epoxycyclohexylmethyl)dicarbamate; isophorone diisocyanate Bis-(3,4-epoxycyclohexylmethyl)dicarbamate; and hexylene-1,6-diisocyanateBis-(3,4-epoxycyclohexylmethyl) dicarbamate.
 9. The epoxy composition ofclaim 1, wherein said organic hardener is a carboxylic acid anhydridehardener.
 10. The epoxy composition of claim 1, further comprising afiller.
 11. The epoxy composition of claim 1, wherein said filler issilica.
 12. The epoxy composition of claim 1, wherein said compositionis thermally degradable at a temperature of less than approximately 250°C.
 13. The epoxy composition of claim 1, wherein said composition isthermally degradable at a temperature between approximately 200 ° C. and250° C.
 14. The epoxy composition of claim 1, wherein said compositionis thermally degradable at a temperature of approximately 220° C.
 15. Amethod of protecting, encapsulating, reinforcing, assembling, orfabricating a device or a chemical product with a cured epoxycomposition which is thermally reworkable, said epoxy compositioncomprising the reaction product of: a thermally degradablecycloaliphatic epoxide; an organic hardener; a curing accelerator; andsilica filler.
 16. The method of claim 15, wherein said cycloaliphaticepoxide contains a carbonate group.
 17. The method of claim 15, whereinsaid cycloaliphatic epoxide is selected from the group consisting of:di-3,4-epoxycyclohexylmethyl carbonate;di-1-(3,4-epoxycyclohexenyl)ethyl carbonate; 3,4-epoxycyclohexylmethylt-butyl carbonate; and 4-epoxyethyllphenyl2-(3-methyl-3,4-epoxycyclohexyl)-2-propyl carbonate.
 18. The method ofclaim 15, wherein said cycloaliphatic epoxide is selected from the groupconsisting of: 3,4-epoxycyclohexyl-1-isocyanate3,4-epoxycyclohexylmethyl carbamate; 3,4-epoxycyclohexyl- 1-isocyanate2-(3,4-epoxycyclohexyl)-2-propyl carbamate; 3,4-epoxycyclohexylmethyl2-(1,2-epoxycyclohexyl)ethyl carbamate; phenylene-1,4-diisocyanateBis-(3,4-epoxycyclohexylmethyl) dicarbamate; tolylene-2,4-diisocyanateBis-(3,4-epoxycyclohexylmethyl) dicarbamate; isophorone diisocyanateBis-(3,4-epoxycyclohexylmethyl) dicarbamate; andhexylene-1,6-diisocyanate Bis-(3,4-epoxycyclohexylmethyl) dicarbamate.19. The method of claim 15, wherein said composition is thermallydegradable at a temperature of less than approximately 250° C.
 20. Themethod of claim 15, wherein said organic hardener is selected from thegroup consisting of: hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl-5-norbomene-2,3-dicarboxylicanhydride, tetrahydrophthalic anhydride, methyl tetrahydrophthalicanhydride, and nadic methyl anhydride; said curing accelerator isselected from the group consisting of: triphenylphosphine,2-ethyl-4-methyl imidazole, 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole,imidazole, 1-methylimidazole, 1-benylimidazole, 1,2-dimethylimidazole,1-benzyl-2-methylimidazole, 4-methyl-2-phenylimidazole,benzyldimethylamine, triethylamine, pyridine, dimethylaminopyridine,1,4-diazabicyclo[2.2.2.]octane, 1,8-diazabicyclo[5.4.0]undec-7-ene, and1,5-diazabicyclo[4.3.0]non-5-ene; and said filler is selected fromsilica fillers with different particle size and particle sizedistribution.